End mills types can be considered to fall within three main end mill categories, namely ball, square and corner radius. The subject matter of the present application relates only to the latter category, corner radius end mills.
A corner of a corner radius end mill comprises a circular arc profile. The circular arc profile is present during rotation of such end mills about a rotation axis when the end mill is viewed in a direction perpendicular to the rotation axis. For the purposes of the specification and claims, this will be called a “profile view”.
The circular arc profile defines a portion of an imaginary circle. The circle defines reference locations including: a circle center point, axial and radial tangent lines, axial and radial tangent points, and a bisector line. The axial tangent line extends forwardly from the circle center point and in a direction parallel with a rotation axis of the end mill. The radial tangent line extends radially outward from the circle center point and in a direction perpendicular with the rotation axis. The bisector line extends outward from the circle center point and intersects the circle at a bisector point equally circumferentially spaced from the axial and radial tangent points. Alternatively stated, a first angle subtended by the bisector line to the axial tangent line and a second angle subtended by the bisector line to the radial tangent line are equal. It will be understood that reference parameters such as the circle and associated lines, planes and tangent points, mentioned above are imaginary and hence are not visible features on an end mill but rather are derivable through the construction thereof as explained above.
Due to a competitive world-wide market, there is ever increasing demand for machining with end mills to provide better finish and longer tool life, even when machining workpieces made of difficult to machine materials such as inconel which quickly degrade an end mill. Such degradation is believed, in theory, to be at least in part due to heat transfer of a workpiece made to an end mill machining the workpiece.
It is believed that by providing a rake ridge at an intersection of rake recessed and rake cutting sub-surfaces, heat transfer to an end mill may be reduced. US 2014/0227050 assigned to the present Applicant discloses, for example in FIG. 1B, an example of such rake sub-surfaces with such rake ridge.